forum configure.py: survive nginx's 429 without a JSON body

The nginx rate limiter in front of Discourse (web.ratelimited) answers 429
with an HTML page, so reading wait_seconds as JSON crashed the script
halfway through creating categories. Fall back to Retry-After or 10 s.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

deploy/forum/configure.py

@@ -89,8 +89,13 @@ def call(method, path, data=None):
                 return json.loads(text) if text else {}
         except urllib.error.HTTPError as error:
             body = error.read().decode()
-            if error.code == 429:  # Discourse rate limit: wait as told, then try again
-                time.sleep(json.loads(body).get("extras", {}).get("wait_seconds", 10) + 1)
+            if error.code == 429:  # rate limit: wait as told, then try again
+                # Rails answers with JSON; the nginx limiter in front (web.ratelimited) with an HTML page.
+                try:
+                    wait = json.loads(body).get("extras", {}).get("wait_seconds", 10)
+                except ValueError:
+                    wait = int(error.headers.get("Retry-After") or 10)
+                time.sleep(wait + 1)
                 continue
             sys.exit(f"{method} {path}: {error.code} {body[:300]}")
     sys.exit(f"{method} {path}: stadig begrænset efter flere forsøg")